We gain knowledge and understanding from a lot of things like experiences, memory, using senses and many others. Past experiences in life help human beings to know and understand new different things, we learn them well and we are able to identify them later because its saved in our memories to remember them again. This process help us through time to know a lot of things. We experience things by using our senses like touching, hearing, looking, tasting and smelling. A simple example to clarify what I've said is, when we look at a vase how do we know its a vase?! By touching it we know what its made of, wood or metal or plastic...etc. By looking at it we know its a vase from its shape and structure. If we saw one before or studied about it in school or even read about it that means we had an experience with it and it is saved in our memory. So when we see a vase again we can tell whether its a vase or not.